[FLINK-34282][docker] Updates snapshot workflow to consider the dev-1.19 branch and new dev-master.

Author: XComp

.github/workflows/snapshot.yml

@@ -38,8 +38,10 @@ jobs:
       matrix:
         java_version: [8, 11]
         build:
-          - flink_version: 1.19-SNAPSHOT
+          - flink_version: 1.20-SNAPSHOT
             branch: dev-master
+          - flink_version: 1.19-SNAPSHOT
+            branch: dev-1.19
           - flink_version: 1.18-SNAPSHOT
             branch: dev-1.18
           - flink_version: 1.17-SNAPSHOT